We have systematically investigated the in-situ growth of $YBa_2Cu_3O_{7-x}$ (YBCO) thin films prepared by pulsed laser deposition, studying the effect of deposition rate at various substrate temperatures on their structural and electrical properties. YBCO thin films were deposited on $SrTiO_3$ (STO) (100) substrate at 650-800℃ by varying the deposition rates in the range of 0.1 nm/s - 12.2 nm/s using different repetition rate of pulsed laser. It was found that depending on the substrate temperature and the deposition rate, the perovskite phases present in the YBCO thin films were quite different. i.e. c-axis oriented orthorhombic phase at high substarte temperature and low deposition rates (800℃, 0.1 nm/s), a-axis orienetd orthorhombic phase at intermediate substrate temperatures and high deposition rates (700℃, 1.3 nm/s-12.2 nm/s), and cubic phase at low substrate temperatures and high deposition rates (650℃, 12.2 nm/s). By using the cross sectional HRTEM and Raman spectroscopy analysis, cation disordered cubic structure was clearly identified.
Also, the expansion of c-lattice parameter and decrease of the critical temperature of YBCO thin films were observed with decreasing the substrate temperature and increasing the deposition rates. The degree of c-lattice parameter expansion and degradation of $T_c$ was increased as the substrate temperature decreased. The c-lattice parameter expansion and $T_c$ decrement was explained by the cation disordering of the Y and Ba atoms in YBCO thin films. In order to apply YBCO thin film to the superconducting field effect transistor, YBCO/STO bi-layer structure was fabricated. In this structure, the oxygen diffusion through the STO capping layer and the stress relaxation in YBCO thin films by inserting PBCO buffer layer are necessary to prevent the decreasing of $T_c$.
Applying the supersaturation and surface mobility concept to the film growth, we were able to explain the deposition rate dependence of the different perovskite phase formation and degradation of film properties.